Elastic moduli,e.g.shear modulus G and bulk modulus K,are important parameters of geotechnical materials,which are not only the indices for the evaluation of the deformation ability of soils but also the important bas...Elastic moduli,e.g.shear modulus G and bulk modulus K,are important parameters of geotechnical materials,which are not only the indices for the evaluation of the deformation ability of soils but also the important basic parameters for the development of the constitutive models of geotechnical materials.In this study,a series of triaxial loading-unloading-reloading shear tests and isotropic loading-unloadingreloading tests are conducted to study several typical mechanical properties of coral calcareous sand(CCS),and the void ratio evolution during loading,unloading and reloading.The test results show that the stress-strain curves during multiple unloading processes are almost parallel,and their slopes are much greater than the deformation modulus at the initial stage of loading.The relationship between the confining pressure and the volumetric strain can be defined approximately by a hyperbolic equation under the condition of monotonic loading of confining pressure.Under the condition of confining pressure unloading,the evolution of void ratio is linear in the e-lnp0 plane,and these lines are a series of almost parallel lines if there are multiple processes of unloading.Based on the experimental results,it is found that the modified Hardin formulae for the elastic modulus estimation have a significant deviation from the tested values for CCS.Based on the experimental results,it is proposed that the elastic modulus of soils should be determined by the intersection line of two spatial surfaces in the G/K-e-p’/pa space(pa:atmosphere pressure).“Ye formulation”is further proposed for the estimation of the elastic modulus of CCS.This new estimation formulation for soil elastic modulus would provide a new method to accurately describe the mechanical behavior of granular soils.展开更多
Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precip...Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.展开更多
Calcareous sand is typically known as a problematic marine sediment because of its diverse morphology and complex inner pore structure.However,the coupling effects of morphology and inner pores on the mechanical prope...Calcareous sand is typically known as a problematic marine sediment because of its diverse morphology and complex inner pore structure.However,the coupling effects of morphology and inner pores on the mechanical properties of calcareous sand particles have rarely been investigated and understood.In this study,apparent contours and internal pore distributions of calcareous sand particles were obtained by three-dimensional(3D)scanning imaging and X-ray micro-computed tomography(X-mCT),respectively.It was revealed that calcareous sand particles with different outer morphologies have different porosities and inner pore distributions because of their original sources and particle transport processes.In addition,a total of 120 photo-related compression tests and 4923D discrete element simulations of four specific shaped particles,i.e.bulky,angular,dendritic and flaky,with variations in the inner pore distribution were conducted.The macroscopic particle strength and Weibull modulus obtained from the physical tests are not positively correlated with the porosity or regularity in shape,indicating the existence of coupling effect of particle shape and pore distribution.The shape effect on the particle strength first increases with the porosity and then decreases.The particle crushing of relatively regular particles is governed by the porosity,but that of extremely irregular particles is governed by the particle shape.The particle strength increases with the uniformity of the pore distribution.Particle fragmentation is mainly dependant on tensile bond strength,and the degree of tensile failure is considerably impacted by the particle shape but limited by the pore distribution.展开更多
BACKGROUND Severe proximal humerus comminuted fractures are often accompanied by medial calcar comminuted fractures and loss of medial support,which are important factors that lead to internal fixation failure.The app...BACKGROUND Severe proximal humerus comminuted fractures are often accompanied by medial calcar comminuted fractures and loss of medial support,which are important factors that lead to internal fixation failure.The appropriate treatment for proximal humerus comminuted fractures has not been established.Therefore,this study assessed the outcomes of using a fibular autograft with locking plates to treat severe proximal humerus comminuted fractures.AIM To investigate the outcomes of using a fibular autograft with locking plates to treat severe proximal humerus comminuted fractures.METHODS This retrospective,comparative cohort study included two groups of patients.Group 1 comprised 22 patients and group 2 comprised 25 patients with complete follow-up data.Group 1 was treated with a fibular autograft with open reduction and locking plates to enable internal fixation.Group 2 was treated with open reduction and locking plates to enable internal fixation.The intraoperative blood loss volume from the shoulder wound,operative time,shoulder wound pain,bone fracture healing time,Constant-Murley score of the shoulder joint,preoperative Holden walking function score,Mallet score of the shoulder joint,and humeral neck-shaft angle during surgery of the two groups were compared,and the differences were analysed using an independent sample t-test.RESULTS Group 1 had a shorter mean operative time than group 2(2.25±0.30 h vs 2.76±0.44 h;P=0.000).Group 1 had a lower shoulder wound pain score on the first day after surgery than group 2(7.91±1.15 points vs 8.56±1.00 points;P=0.044).Group 1 had a shorter fracture healing time than group 2(2.68±0.48 mo vs 3.64±0.64 mo;P=0.000).Group 1 had higher Constant-Murley scores of the shoulder joint at 3,6,and 12 mo after surgery than group 2(76.64±4.02 points vs 72.72±3.02 points,86.36±3.53 points vs 82.96±3.40 points,and 87.95±2.77 points vs 84.68±2.63 points,respectively;P=0.000,0.002,and 0.000,respectively).Group 1 had higher Mallet scores of the shoulder joint at 3,6,and 12 mo after surgery than group 2(10.32±0.57 points vs 9.96±0.54 points,13.36±1.00 points vs 12.60±0.87 points,and 13.91±0.75 points vs 13.36±0.70 points,respectively;P=0.032,0.007,and 0.013,respectively).CONCLUSION Using locking plates with a fibular autograft can recreate medial support,facilitate fracture healing,and improve shoulder function;therefore,this may be an effective treatment option for severe proximal humerus comminuted fractures.展开更多
Currently in Niu-zhuang sub-sag, the seismic reflection amplitude of the newly discovered turbidite sandstone is stronger in the third Segment. The main reason is that Calcareous components accounts for a large part a...Currently in Niu-zhuang sub-sag, the seismic reflection amplitude of the newly discovered turbidite sandstone is stronger in the third Segment. The main reason is that Calcareous components accounts for a large part and physical properties is relatively poor, which results in no corresponding relation between reservoir and seismic attributes, and effective reservoir is difficult to predict and describe. Therefore, using the method of geological statistics, we firstly study the distribution of calcareous matters, secondly study the contribution to seismic reflection amplitude made by Calcareous high impedance component;thirdly analyze its influence on actual seismic reflection amplitude and determine the lithology thickness of Calcareous via replacement forward modeling. At last, we characterize the reservoir using the amplitude of calcareous matters. It proves that the method of seismic-geological comprehensive prediction is reliable. It has good guidance for exploration and development of the calcareous sand lithologic reservoir in similar areas.展开更多
It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yiel...It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yield and soil properties in a calcareous soil. Five treatments were: 1) straw incorporation; 2) straw incorporation with inorganic fertilizer; 3), 4) and 5) straw incorporation with inorganic fertilizer, and biochar at 30, 60, and 90 t ha-l, respectively. The annual yield of either winter wheat or summer maize was not increased significantly following biochar application, whereas the cumulative yield over the first 4 growing seasons was significantly increased. Soil pH, measured in situ, was increased by a maximum of 0.35 units after 2 yr following biochar application. After 3 yr, soil bulk density significantly decreased while soil water holding capacity increased with adding biochar of 90 t ha^-1. Alkaline hydrolysable N decreased but exchangeable K increased due to biochar addition. Olsen-P did not change compared to the treatment without biochar. The results suggested that biochar could be used in calcareous soils without yield loss or significant impacts on nutrient availability.展开更多
Calcareous sand has distinct characteristics in comparison with silica sand, such as dynamic behavior at high strain rates(HSRs). This is closely related to pile driving, aircraft wheel loading and mining activities. ...Calcareous sand has distinct characteristics in comparison with silica sand, such as dynamic behavior at high strain rates(HSRs). This is closely related to pile driving, aircraft wheel loading and mining activities. To understand the response of calcareous sand at HSRs, a series of dynamic tests is performed using the split Hopkinson pressure bar(SHPB) with steel sleeve, including 6 validation tests of bar-against-bar and 16 comparative tests relevant to the relative density and strain rate of calcareous and silica sands.The apparent dynamic stiffness of calcareous sand is approximately 10% of that for silica sand due to different particle shapes and mineral compositions. The axial stress-strain response of silica sand is mainly governed by the deformation of individual grain and soil skeleton, and particle crushing. However, porous calcareous sand shows yielding and strain-hardening responses that are always followed by particle crushing. As the applied loading increases, the particle crushing of calcareous sand develops from local instability to whole breakage. Calcareous sand has lower viscous flow effects compared with silica sand at HSRs.展开更多
The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwest...The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.展开更多
A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age. The bio-imprinting of ca...A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age. The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous, late Paleocene, (early, middle, late) Eocene, middle Miocene, late Pliocene, and Pleistocene. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were used to test the Co-rich crusts, and a variety of molecular fossils were detected, such as chloroform bituminous "A" , n-alkane, isoprenoid and sterol. Peak carbon and molecular indices (such as C23-/C24+, CPI, Pr/Ph, Pr/nC17, Ph/nCxs and j13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter. Researches on calcareous nannofossils, molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene (P/E) global event is recorded in the cobalt- rich crusts from the northwestern Pacific Ocean. A succession of biomes can be observed near the 85 mm boundary (about 55 Ma), i.e., the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis, and Broisonia parka microbiotas above the P/E boundary, and the bloom of Coccolithus formosus, Discoaster multiradiatus, Discoaster mohleri and Discoaster sp. below the boundary. Typical parameters of molecular fossils, such as saturated hydrocarbon components and carbon-number maxima, Pr/Ph, Pr/C17, Ph/C18, distribution types of sterols, Ts/Tm ratios and bacterial hopane, also exhibit dramatic changes near the P/E boundary. These integrated results illustrate that the biome succession of calcareous nannofossils, relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event.展开更多
To better understand the mechanism of the strength weakening process of soft rocks in deep mines after interacting with water, a self-developed experimental system, Intelligent Testing System for Water Absorption in D...To better understand the mechanism of the strength weakening process of soft rocks in deep mines after interacting with water, a self-developed experimental system, Intelligent Testing System for Water Absorption in Deep Soft Rocks (ITSWADSR), is employed to analyze the hydrophilic behavior of deep calcareous shale sampled from Daqiang coal mine. Experimental results demonstrate that the relation between water absorption and time can be expressed by power functions, and the soakage rate decreases while the soakage increases with time. In order to quantitatively calculate the weight coefficients of the influential factors for water absorbing capacity of rocks, a series of testing methods are adopted, including scanning electron microscope (SEM), X-ray diffraction and mercury injection test. It is demonstrated that the effective porosity has a positive correlation with the water absorbing capacity of rocks and the contents of illite and illite/smectite. The initial water content presents a negative correlation with the water absorption capacity of rocks. According to the absolute value of weight coefficients of various influential factors, the order of magnitude from high to low is captured: initial water content, illite, illite/smectite formation (S=5%), and the effective porosity. After water absorption tests, uniaxial compressive strength (UCS) tests were performed on rock specimens allowing a linear relationship between the UCS and the water content of rock to be established, indicating that the strength of calcareous shale decreases linearly with the increasing water content.展开更多
The basic features and acoustic-physical properties of calcareous seafloor soils in the tropic sea area are obviously different from those of sediments mainly composed of terrigenous materials in the South China Sea. ...The basic features and acoustic-physical properties of calcareous seafloor soils in the tropic sea area are obviously different from those of sediments mainly composed of terrigenous materials in the South China Sea. Generally calcareous soils, composed of carbonate particles of marine organism remains. have the characteristics of high water content, high porosity, low wet density, high sound velocity and greatly varied comprehensive strength. Recognizing the differences between calcareous soils and terrigenous sediments and engineering geologic significance of calcareous soils is crucial for seafloor geologic research and geotechnical survey for pile-jacket platform foundation design.展开更多
The middle Cretaceous Kazhdumi Formation,with a thickness of 222 m,belongs to the Bangestan Group and occurs in the Zagros folded zone in southwest Iran.The lower boundary with the Dariyan Formation is disconformable,...The middle Cretaceous Kazhdumi Formation,with a thickness of 222 m,belongs to the Bangestan Group and occurs in the Zagros folded zone in southwest Iran.The lower boundary with the Dariyan Formation is disconformable,which is recognized by iron oxides and glauconite.The recognized microfossils are Valvulammina sp.,Scandonea sp.,Daxia cenomana,Choffatela sp., Pseudolituonella reicheli and calcareous algae-Lithocodium aggregation(which belongs to the Sarvak Formation),representing the beginning of Cenomanian.Other microfossils are:Ammobaculites goodlandensis,Marsonella trochus,Hemicyclammina sigali,Praechrysalidina infracretacea,Orbitolina gr.concava,Orbitolina(conicorbitolina)conica,Orbitolina subconcava,Salpingoporella sp.,Trinocladus tripolitanus,Trinocladus sp.,Permocalculus irenae and Dissocladella deserta.These microfossils can be classified into five assemblage zones.展开更多
Calcareous soil contains organic and inorganic carbon(C) pools,which both contribute to CO2 emission during closed-jar incubation. The mineralization of organic C and dissolution of inorganic C are both related to so...Calcareous soil contains organic and inorganic carbon(C) pools,which both contribute to CO2 emission during closed-jar incubation. The mineralization of organic C and dissolution of inorganic C are both related to soil moisture,but the exact effect of water content on CO2 emission from calcareous soil is unclear. The objective of this experiment was to determine the effect of soil water content(air-dried,30%,70%,and 100% water-holding capacity(WHC)),carbonate type(CaCO3 or MgCO3),and carbonate amount(0.0,1.0%,and 2.0%) on CO2 emission from calcareous soil during closed-jar incubation. Soil CO2 emission increased significantly as the water content increased to 70% WHC,regardless of whether or not the soil was amended with carbonates. Soil CO2 emission remained the same or increased slowly as the soil water content increased from 70% WHC to 100% WHC. When the water content was ≤30% WHC,soil CO2 emission from soil amended with 1.0% inorganic C was greater than that from unamended soil. When the soil water content was 70% or 100% WHC,CO2 emission from CaCO3 amended soil was greater than that from the control. Furthermore,CO2 emission from soil amended with 2.0% CaCO3 was greater than that from soil amended with 1.0% CaCO3. Soil CO2 emission was higher in the MgCO3 amended soil than from the unamended soil. Soil CO2 emission decreased as the MgCO3 content increased. Cumulative CO2 emission was 3-6 times higher from MgCO3 amended soil than from CaCO3 amended soil. There was significant interaction effect between soil moisture and carbonates on CO2 emission. Soil moisture plays an important role in CO2 emission from calcareous soil because it affects both biotic and abiotic processes during the closed-jar incubation.展开更多
The influence of dissolved oxygen on calcareous deposits formed under galvanostatic polarization mode was studied.When the dissolved oxygen concentration was less than 7 mg L^(-1),the cathodic protection potential sho...The influence of dissolved oxygen on calcareous deposits formed under galvanostatic polarization mode was studied.When the dissolved oxygen concentration was less than 7 mg L^(-1),the cathodic protection potential showed a plateau at the initial polarization,and then quickly shifted negatively.While the dissolved oxygen was more than 9 mg L^(-1),the potential shifted negatively in a linear form.After 168 h of polarization,the final protection potential shifted negatively with the decreasing dissolved oxygen concentration.The deposition progress was monitored by electrochemical impedance spectroscopy,and only one single loop was found in Nyquist diagram,indicating deposits of ineffective protectiveness precipitation under the experimental conditions.The protection factor of deposits increased with the decreasing dissolved oxygen concentration which was detected by linear polarization resistance technique.The cathodic electrochemical reaction could change very shortly from oxygen reduction to hydrogen evolution after cathodic protection under very low dissolved oxygen concentration,such as 1 mg L^(-1),resulting in the hydrogen bubbling from the metallic surface and the decrease of deposits protection factor.Observation by scanning electron microscopy and X-ray diffraction analysis demonstrated that the deposits were mainly of calcite under the experimental conditions,and that dissolved oxygen had no effect on the crystalline types of calcium carbonate.展开更多
The quantity of soil microbes and the structure of ammonium oxidizing bacterial (AOB) community were analyzed using the dilution plate counting and most probable number method (MPN), and denaturing gradient gel el...The quantity of soil microbes and the structure of ammonium oxidizing bacterial (AOB) community were analyzed using the dilution plate counting and most probable number method (MPN), and denaturing gradient gel electrophoresis (DGGE), respectively. Fertilizer application tended to increase the number of soil microbes and alter the AOB community compared to the control with no fertilizer application (CK). Among the eight fertilizer treatments, soil samples from the treatments of mineral fertilizers (e.g., N, P, K) in combination with farmyard manure (M) had greater number.s of soil microbes and more complex structure of AOB community than those receiving mineral fertilizers alone. The principal component analyses (PCA) for ammonium oxidizing bacterial community structure showed that the eight fertilizer treatments could be divided into two PCA groups (PCA1 and PCA2). For the soil sampled after rice harvest, PCA1 included NP, NM, NPM and NPKM fertilizer treatments, while PCA2 was consisted of CK, N, M and NPK fertilizer treatments. For soil samples collected after wheat harvest, PCA1 was consisted of M, NM, NPM and NPKM fertilizer treatments, while PCA2 was composed of CK, N, NP and NPK fertilizer treatments. For a given rotation, the richness of AOB community in PCA1 was greater than that in PCA2. In addition, AOB community structure was more complex in the soil after rice harvest than that after wheat harvest. The results indicated that different fertilizer treatments resulted in substantial changes of soil microbe number and AOB community. Furthermore, mineral fertilizers (N, NP, NPK) combined with farmyard manure were effective for increasing the quantity of soil microbes, enriching AOB community, and improving the soil biofertility.展开更多
A biostratigraphic study of calcareous nannofossils of sediments from Lingfeng No.1 well in the East China Sea was carried out to provide more detailed nannofossil data and a stratigraphic correlation among offshore ...A biostratigraphic study of calcareous nannofossils of sediments from Lingfeng No.1 well in the East China Sea was carried out to provide more detailed nannofossil data and a stratigraphic correlation among offshore wells located in the East China Sea.14 Paleocene to Pleistocene calcareous nannofossil zones were recognized based on a detailed examination. According to these nannofossil data, the Paleocene/Eocene and Pliocene/Pleistocene boundaries, as well as the Miocene base were determined.Oligocene NP23 and Miocene NN1 zones are firstly recognized by this study. The existence of Miocene NN1 at this well suggests that the Miocene transgression began in the Early Miocene in this area. The records of NP23 indicate that the marine Oligocene sediments exist in the series of Lingfeng wells, but probably as very thin layers.展开更多
Investigation of dynamic properties of carbonate/calcareous soils is important in earthquake and offshore engineering as these soils are commonly encountered in large-scale projects related with energy geomechanics an...Investigation of dynamic properties of carbonate/calcareous soils is important in earthquake and offshore engineering as these soils are commonly encountered in large-scale projects related with energy geomechanics and land reclamation.In this study,the stiffness and stiffness anisotropy of two types of calcareous sands(CS)from the Western Australia and the Philippines were examined using bender elements configured in different directions in stress path setups.Stiffness measurements were taken on specimens subjected to constant p’compression/extension and biaxial stress paths and additional tests were performed on three types of silica sands with different geological origins and particle shapes,which were used as benchmark materials in the study.Compared with the three brands of silica sands,the stiffness of the CS was found to be more significantly influenced by anisotropic loading;an important observation of the experimental results was that stress anisotropy had different weighted influences on the stiffness in different directions,thus influencing stiffness anisotropy.Comparisons were made between the specimens subjected to complex loading paths,and respected model parameters as suggested from published expressions in the literature.These comparisons further highlighted that calcareous soils have different responses in terms of stiffness,stiffness anisotropy and loading history,compared with that of silica-based sands.展开更多
The shear strength and dilatancy of typical uncemented calcareous sand from the South China Sea are investigated by soil lab tests.According to drained triaxial tests at various relative densities and confining stress...The shear strength and dilatancy of typical uncemented calcareous sand from the South China Sea are investigated by soil lab tests.According to drained triaxial tests at various relative densities and confining stresses,it is found that the constant volume friction angle is approximated as 39°and the traditional Bolton’s equations can be modified to estimate the peak friction angle and dilation angle.The reliability of the equation proposed for the peak friction angle is verified in terms of calcareous sands from more onshore and offshore sites worldwide,while the errors of the predicted dilation angles scatter in a relatively large range.Totally,the dilation angles of sands in the South China Sea are estimated by the equation presented with an error of±30%.The peak friction angle measured by the undrained is similar to that by the drained tests as the relative density smaller than 60%,while the former is slightly lower for denser samples.展开更多
Cathodic protection is a very effective method to protect metals, which can form calcareous deposits on metal surface. Research on the interrelationship between fouling organism and calcareous deposits is very importa...Cathodic protection is a very effective method to protect metals, which can form calcareous deposits on metal surface. Research on the interrelationship between fouling organism and calcareous deposits is very important but very limited, especially sulfate-reducing bacteria(SRB). SRB is a kind of very important fouling organism that causes microbial corrosion of metals. A study of the influence of calcareous deposit on corrosion behavior of Q235 carbon steel in SRB-containing culture medium was carried out using electrochemical impedance spectroscopy(EIS), scanning electron microscopy(SEM) and surface spectroscopy(EDS). The calcareous deposit was formed with good crystallinity and smooth surface under the gradient current density of -30 μA cm^(-2) in natural seawater for 72 h. Our results can help elucidate the formation of calcareous deposits and reveal the interrelationship between SRB and calcareous deposits under cathodic protection. The results indicate that the corrosion tendency of carbon steel was obviously affected by Sulfate-reducing Bacteria(SRB) metabolic activity and the calcareous deposit formed on the surface of carbon steel under cathodic protection was favourable to reduce the corrosion rate. Calcareous deposits can promote bacterial adhesion before biofilm formation. The results revealed the interaction between biofouling and calcareous deposits, and the anti-corrosion ability was enhanced by a kind of inorganic and organic composite membranes formed by biofilm and calcareous deposits.展开更多
Soil organic carbon(SOC)plays a key role in improving soil quality and optimizing crop yield.Yet little is known about the fate of macroaggregates(>0.25 mm)under long-term fertilization and their relative importanc...Soil organic carbon(SOC)plays a key role in improving soil quality and optimizing crop yield.Yet little is known about the fate of macroaggregates(>0.25 mm)under long-term fertilization and their relative importance in SOC sequestration in reclaimed calcareous soil.Therefore,the effects of mineral fertilizers and organic manure on the mechanisms of organic carbon(OC)stabilization in macroaggregates were investigated in this study.Four treatments were used:unfertilized control(CK),mineral fertilizer(NPK),compost chicken manure alone(M),and mineral fertilizers plus manure(MNPK).Samples from the 0–20 cm layer of soil receiving 11-year-long fertilization were separated into four fractions based on the macroaggregates present(unprotected coarse and fine particulate organic matter,cPOM and fPOM;physically protected intra-microaggregate POM,i POM;and biochemically protected mineral associated OM,MOM)by the physical fractionation method.Compared with the control,the long-term application of NPK had little effect on SOC content,total nitrogen(TN)content,and OC and TN contents of macroaggregate fractions.In contrast,incorporation of organic manure(MNPK)significantly increased SOC(45.7%)and TN(24.3%)contents.Application of MNPK increased OC contents within macroaggregate-extracted fractions of cPOM(292.2%),fPOM(136.0%)and iPOM(124.0%),and TN contents within cPOM(607.1%),fPOM(242.5%)and iPOM(127.6%),but not the mineral associated organic carbon(MOM-C)and nitrogen(MOM-N)contents.Unprotected C fractions were more strongly and positively correlated with SOC increase than protected C fractions,especially for cPOM-C,indicating that SOC sequestration mainly occurred via cPOM-C in the studied calcareous soil.In conclusion,MNPK increased the quantity and stability of SOC by increasing the contents of cPOM-C and cPOM-N,suggesting that this management practice(MNPK)is an effective strategy to develop sustainable agriculture.展开更多
基金Professor Jianhong Ye is grateful for the funding support from the National Key Research and Development Program of China(Grant No.2022YFC3102402).
文摘Elastic moduli,e.g.shear modulus G and bulk modulus K,are important parameters of geotechnical materials,which are not only the indices for the evaluation of the deformation ability of soils but also the important basic parameters for the development of the constitutive models of geotechnical materials.In this study,a series of triaxial loading-unloading-reloading shear tests and isotropic loading-unloadingreloading tests are conducted to study several typical mechanical properties of coral calcareous sand(CCS),and the void ratio evolution during loading,unloading and reloading.The test results show that the stress-strain curves during multiple unloading processes are almost parallel,and their slopes are much greater than the deformation modulus at the initial stage of loading.The relationship between the confining pressure and the volumetric strain can be defined approximately by a hyperbolic equation under the condition of monotonic loading of confining pressure.Under the condition of confining pressure unloading,the evolution of void ratio is linear in the e-lnp0 plane,and these lines are a series of almost parallel lines if there are multiple processes of unloading.Based on the experimental results,it is found that the modified Hardin formulae for the elastic modulus estimation have a significant deviation from the tested values for CCS.Based on the experimental results,it is proposed that the elastic modulus of soils should be determined by the intersection line of two spatial surfaces in the G/K-e-p’/pa space(pa:atmosphere pressure).“Ye formulation”is further proposed for the estimation of the elastic modulus of CCS.This new estimation formulation for soil elastic modulus would provide a new method to accurately describe the mechanical behavior of granular soils.
基金This study was financially supported by the Natural Science Foundation of China(Grant No.42007246)the Fundamental Research Funds for the Central Universities(Grant No.2242022k30055)Indo-U.S.Science and Technology Forum(Grant No.IUSSTF/AUG/JC/047/2018).
文摘Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.
基金the Fundamental Research Funds for the Central Universities,China(Grant No.B210203032)the National Natural Science Foundation of China(Grant No.52279097)the Green and Blue Project of Jiangsu Province,China.
文摘Calcareous sand is typically known as a problematic marine sediment because of its diverse morphology and complex inner pore structure.However,the coupling effects of morphology and inner pores on the mechanical properties of calcareous sand particles have rarely been investigated and understood.In this study,apparent contours and internal pore distributions of calcareous sand particles were obtained by three-dimensional(3D)scanning imaging and X-ray micro-computed tomography(X-mCT),respectively.It was revealed that calcareous sand particles with different outer morphologies have different porosities and inner pore distributions because of their original sources and particle transport processes.In addition,a total of 120 photo-related compression tests and 4923D discrete element simulations of four specific shaped particles,i.e.bulky,angular,dendritic and flaky,with variations in the inner pore distribution were conducted.The macroscopic particle strength and Weibull modulus obtained from the physical tests are not positively correlated with the porosity or regularity in shape,indicating the existence of coupling effect of particle shape and pore distribution.The shape effect on the particle strength first increases with the porosity and then decreases.The particle crushing of relatively regular particles is governed by the porosity,but that of extremely irregular particles is governed by the particle shape.The particle strength increases with the uniformity of the pore distribution.Particle fragmentation is mainly dependant on tensile bond strength,and the degree of tensile failure is considerably impacted by the particle shape but limited by the pore distribution.
文摘BACKGROUND Severe proximal humerus comminuted fractures are often accompanied by medial calcar comminuted fractures and loss of medial support,which are important factors that lead to internal fixation failure.The appropriate treatment for proximal humerus comminuted fractures has not been established.Therefore,this study assessed the outcomes of using a fibular autograft with locking plates to treat severe proximal humerus comminuted fractures.AIM To investigate the outcomes of using a fibular autograft with locking plates to treat severe proximal humerus comminuted fractures.METHODS This retrospective,comparative cohort study included two groups of patients.Group 1 comprised 22 patients and group 2 comprised 25 patients with complete follow-up data.Group 1 was treated with a fibular autograft with open reduction and locking plates to enable internal fixation.Group 2 was treated with open reduction and locking plates to enable internal fixation.The intraoperative blood loss volume from the shoulder wound,operative time,shoulder wound pain,bone fracture healing time,Constant-Murley score of the shoulder joint,preoperative Holden walking function score,Mallet score of the shoulder joint,and humeral neck-shaft angle during surgery of the two groups were compared,and the differences were analysed using an independent sample t-test.RESULTS Group 1 had a shorter mean operative time than group 2(2.25±0.30 h vs 2.76±0.44 h;P=0.000).Group 1 had a lower shoulder wound pain score on the first day after surgery than group 2(7.91±1.15 points vs 8.56±1.00 points;P=0.044).Group 1 had a shorter fracture healing time than group 2(2.68±0.48 mo vs 3.64±0.64 mo;P=0.000).Group 1 had higher Constant-Murley scores of the shoulder joint at 3,6,and 12 mo after surgery than group 2(76.64±4.02 points vs 72.72±3.02 points,86.36±3.53 points vs 82.96±3.40 points,and 87.95±2.77 points vs 84.68±2.63 points,respectively;P=0.000,0.002,and 0.000,respectively).Group 1 had higher Mallet scores of the shoulder joint at 3,6,and 12 mo after surgery than group 2(10.32±0.57 points vs 9.96±0.54 points,13.36±1.00 points vs 12.60±0.87 points,and 13.91±0.75 points vs 13.36±0.70 points,respectively;P=0.032,0.007,and 0.013,respectively).CONCLUSION Using locking plates with a fibular autograft can recreate medial support,facilitate fracture healing,and improve shoulder function;therefore,this may be an effective treatment option for severe proximal humerus comminuted fractures.
文摘Currently in Niu-zhuang sub-sag, the seismic reflection amplitude of the newly discovered turbidite sandstone is stronger in the third Segment. The main reason is that Calcareous components accounts for a large part and physical properties is relatively poor, which results in no corresponding relation between reservoir and seismic attributes, and effective reservoir is difficult to predict and describe. Therefore, using the method of geological statistics, we firstly study the distribution of calcareous matters, secondly study the contribution to seismic reflection amplitude made by Calcareous high impedance component;thirdly analyze its influence on actual seismic reflection amplitude and determine the lithology thickness of Calcareous via replacement forward modeling. At last, we characterize the reservoir using the amplitude of calcareous matters. It proves that the method of seismic-geological comprehensive prediction is reliable. It has good guidance for exploration and development of the calcareous sand lithologic reservoir in similar areas.
基金financially supported by the National Natural Science Foundation of China (41171211)
文摘It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yield and soil properties in a calcareous soil. Five treatments were: 1) straw incorporation; 2) straw incorporation with inorganic fertilizer; 3), 4) and 5) straw incorporation with inorganic fertilizer, and biochar at 30, 60, and 90 t ha-l, respectively. The annual yield of either winter wheat or summer maize was not increased significantly following biochar application, whereas the cumulative yield over the first 4 growing seasons was significantly increased. Soil pH, measured in situ, was increased by a maximum of 0.35 units after 2 yr following biochar application. After 3 yr, soil bulk density significantly decreased while soil water holding capacity increased with adding biochar of 90 t ha^-1. Alkaline hydrolysable N decreased but exchangeable K increased due to biochar addition. Olsen-P did not change compared to the treatment without biochar. The results suggested that biochar could be used in calcareous soils without yield loss or significant impacts on nutrient availability.
基金the support of the National Natural Science Foundation of China(Grant Nos.51779264and 51408607)the Natural Science Foundation of Jiangsu Province(Grant No.BK20171399)+1 种基金the Hong Kong Scholars Program(Grant No.2016QNRC001)the Young Elite Scientist Sponsorship(Grant No.17-JCJQ-QT-021)
文摘Calcareous sand has distinct characteristics in comparison with silica sand, such as dynamic behavior at high strain rates(HSRs). This is closely related to pile driving, aircraft wheel loading and mining activities. To understand the response of calcareous sand at HSRs, a series of dynamic tests is performed using the split Hopkinson pressure bar(SHPB) with steel sleeve, including 6 validation tests of bar-against-bar and 16 comparative tests relevant to the relative density and strain rate of calcareous and silica sands.The apparent dynamic stiffness of calcareous sand is approximately 10% of that for silica sand due to different particle shapes and mineral compositions. The axial stress-strain response of silica sand is mainly governed by the deformation of individual grain and soil skeleton, and particle crushing. However, porous calcareous sand shows yielding and strain-hardening responses that are always followed by particle crushing. As the applied loading increases, the particle crushing of calcareous sand develops from local instability to whole breakage. Calcareous sand has lower viscous flow effects compared with silica sand at HSRs.
基金financially supported in part by funds from the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) (GBL215010)National Basic Research Program of China (973 Program, No. 2012CB822002)+3 种基金the National Natural Science Foundation of China (Nos. 41302008, 41172037)the Fundamental Research Funds for the Central Universities (53200859490)Science and Technology Innovation Fund of the China University of Geoscience (Beijing)the Beijing Higher Education Young Elite Teacher Project (YETP0665)
文摘The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.
基金supported by National Natural Science Foundation of China (Grant Nos. 41076072 and 40676025)
文摘A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age. The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous, late Paleocene, (early, middle, late) Eocene, middle Miocene, late Pliocene, and Pleistocene. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were used to test the Co-rich crusts, and a variety of molecular fossils were detected, such as chloroform bituminous "A" , n-alkane, isoprenoid and sterol. Peak carbon and molecular indices (such as C23-/C24+, CPI, Pr/Ph, Pr/nC17, Ph/nCxs and j13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter. Researches on calcareous nannofossils, molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene (P/E) global event is recorded in the cobalt- rich crusts from the northwestern Pacific Ocean. A succession of biomes can be observed near the 85 mm boundary (about 55 Ma), i.e., the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis, and Broisonia parka microbiotas above the P/E boundary, and the bloom of Coccolithus formosus, Discoaster multiradiatus, Discoaster mohleri and Discoaster sp. below the boundary. Typical parameters of molecular fossils, such as saturated hydrocarbon components and carbon-number maxima, Pr/Ph, Pr/C17, Ph/C18, distribution types of sterols, Ts/Tm ratios and bacterial hopane, also exhibit dramatic changes near the P/E boundary. These integrated results illustrate that the biome succession of calcareous nannofossils, relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event.
基金Supported by the Key Basic Research Program of China(2006CB202200)the National Major Project of Ministry of Education of China(304005)
文摘To better understand the mechanism of the strength weakening process of soft rocks in deep mines after interacting with water, a self-developed experimental system, Intelligent Testing System for Water Absorption in Deep Soft Rocks (ITSWADSR), is employed to analyze the hydrophilic behavior of deep calcareous shale sampled from Daqiang coal mine. Experimental results demonstrate that the relation between water absorption and time can be expressed by power functions, and the soakage rate decreases while the soakage increases with time. In order to quantitatively calculate the weight coefficients of the influential factors for water absorbing capacity of rocks, a series of testing methods are adopted, including scanning electron microscope (SEM), X-ray diffraction and mercury injection test. It is demonstrated that the effective porosity has a positive correlation with the water absorbing capacity of rocks and the contents of illite and illite/smectite. The initial water content presents a negative correlation with the water absorption capacity of rocks. According to the absolute value of weight coefficients of various influential factors, the order of magnitude from high to low is captured: initial water content, illite, illite/smectite formation (S=5%), and the effective porosity. After water absorption tests, uniaxial compressive strength (UCS) tests were performed on rock specimens allowing a linear relationship between the UCS and the water content of rock to be established, indicating that the strength of calcareous shale decreases linearly with the increasing water content.
基金This project was financially supported by the National Natrual Science Foundation of China(No.49676286)
文摘The basic features and acoustic-physical properties of calcareous seafloor soils in the tropic sea area are obviously different from those of sediments mainly composed of terrigenous materials in the South China Sea. Generally calcareous soils, composed of carbonate particles of marine organism remains. have the characteristics of high water content, high porosity, low wet density, high sound velocity and greatly varied comprehensive strength. Recognizing the differences between calcareous soils and terrigenous sediments and engineering geologic significance of calcareous soils is crucial for seafloor geologic research and geotechnical survey for pile-jacket platform foundation design.
文摘The middle Cretaceous Kazhdumi Formation,with a thickness of 222 m,belongs to the Bangestan Group and occurs in the Zagros folded zone in southwest Iran.The lower boundary with the Dariyan Formation is disconformable,which is recognized by iron oxides and glauconite.The recognized microfossils are Valvulammina sp.,Scandonea sp.,Daxia cenomana,Choffatela sp., Pseudolituonella reicheli and calcareous algae-Lithocodium aggregation(which belongs to the Sarvak Formation),representing the beginning of Cenomanian.Other microfossils are:Ammobaculites goodlandensis,Marsonella trochus,Hemicyclammina sigali,Praechrysalidina infracretacea,Orbitolina gr.concava,Orbitolina(conicorbitolina)conica,Orbitolina subconcava,Salpingoporella sp.,Trinocladus tripolitanus,Trinocladus sp.,Permocalculus irenae and Dissocladella deserta.These microfossils can be classified into five assemblage zones.
基金supported by the National Natural Science Foundation of China(40773057)the National Technology R&D Pillar Program in the 12th Five-Year Plan of China(2012BAD15B04)
文摘Calcareous soil contains organic and inorganic carbon(C) pools,which both contribute to CO2 emission during closed-jar incubation. The mineralization of organic C and dissolution of inorganic C are both related to soil moisture,but the exact effect of water content on CO2 emission from calcareous soil is unclear. The objective of this experiment was to determine the effect of soil water content(air-dried,30%,70%,and 100% water-holding capacity(WHC)),carbonate type(CaCO3 or MgCO3),and carbonate amount(0.0,1.0%,and 2.0%) on CO2 emission from calcareous soil during closed-jar incubation. Soil CO2 emission increased significantly as the water content increased to 70% WHC,regardless of whether or not the soil was amended with carbonates. Soil CO2 emission remained the same or increased slowly as the soil water content increased from 70% WHC to 100% WHC. When the water content was ≤30% WHC,soil CO2 emission from soil amended with 1.0% inorganic C was greater than that from unamended soil. When the soil water content was 70% or 100% WHC,CO2 emission from CaCO3 amended soil was greater than that from the control. Furthermore,CO2 emission from soil amended with 2.0% CaCO3 was greater than that from soil amended with 1.0% CaCO3. Soil CO2 emission was higher in the MgCO3 amended soil than from the unamended soil. Soil CO2 emission decreased as the MgCO3 content increased. Cumulative CO2 emission was 3-6 times higher from MgCO3 amended soil than from CaCO3 amended soil. There was significant interaction effect between soil moisture and carbonates on CO2 emission. Soil moisture plays an important role in CO2 emission from calcareous soil because it affects both biotic and abiotic processes during the closed-jar incubation.
基金the financial support of this project by the National Basic Research Program of China(973 Project,No.2014CB643300)National Environmental Corrosion Platform(NECP)
文摘The influence of dissolved oxygen on calcareous deposits formed under galvanostatic polarization mode was studied.When the dissolved oxygen concentration was less than 7 mg L^(-1),the cathodic protection potential showed a plateau at the initial polarization,and then quickly shifted negatively.While the dissolved oxygen was more than 9 mg L^(-1),the potential shifted negatively in a linear form.After 168 h of polarization,the final protection potential shifted negatively with the decreasing dissolved oxygen concentration.The deposition progress was monitored by electrochemical impedance spectroscopy,and only one single loop was found in Nyquist diagram,indicating deposits of ineffective protectiveness precipitation under the experimental conditions.The protection factor of deposits increased with the decreasing dissolved oxygen concentration which was detected by linear polarization resistance technique.The cathodic electrochemical reaction could change very shortly from oxygen reduction to hydrogen evolution after cathodic protection under very low dissolved oxygen concentration,such as 1 mg L^(-1),resulting in the hydrogen bubbling from the metallic surface and the decrease of deposits protection factor.Observation by scanning electron microscopy and X-ray diffraction analysis demonstrated that the deposits were mainly of calcite under the experimental conditions,and that dissolved oxygen had no effect on the crystalline types of calcium carbonate.
基金the National Key Technology R&D Program of China (2006BAD05B06 and 2006BAD 02A14-13)
文摘The quantity of soil microbes and the structure of ammonium oxidizing bacterial (AOB) community were analyzed using the dilution plate counting and most probable number method (MPN), and denaturing gradient gel electrophoresis (DGGE), respectively. Fertilizer application tended to increase the number of soil microbes and alter the AOB community compared to the control with no fertilizer application (CK). Among the eight fertilizer treatments, soil samples from the treatments of mineral fertilizers (e.g., N, P, K) in combination with farmyard manure (M) had greater number.s of soil microbes and more complex structure of AOB community than those receiving mineral fertilizers alone. The principal component analyses (PCA) for ammonium oxidizing bacterial community structure showed that the eight fertilizer treatments could be divided into two PCA groups (PCA1 and PCA2). For the soil sampled after rice harvest, PCA1 included NP, NM, NPM and NPKM fertilizer treatments, while PCA2 was consisted of CK, N, M and NPK fertilizer treatments. For soil samples collected after wheat harvest, PCA1 was consisted of M, NM, NPM and NPKM fertilizer treatments, while PCA2 was composed of CK, N, NP and NPK fertilizer treatments. For a given rotation, the richness of AOB community in PCA1 was greater than that in PCA2. In addition, AOB community structure was more complex in the soil after rice harvest than that after wheat harvest. The results indicated that different fertilizer treatments resulted in substantial changes of soil microbe number and AOB community. Furthermore, mineral fertilizers (N, NP, NPK) combined with farmyard manure were effective for increasing the quantity of soil microbes, enriching AOB community, and improving the soil biofertility.
基金This study is supported by the National Natural Science Foundation of China( No.49772 12 3 )
文摘A biostratigraphic study of calcareous nannofossils of sediments from Lingfeng No.1 well in the East China Sea was carried out to provide more detailed nannofossil data and a stratigraphic correlation among offshore wells located in the East China Sea.14 Paleocene to Pleistocene calcareous nannofossil zones were recognized based on a detailed examination. According to these nannofossil data, the Paleocene/Eocene and Pliocene/Pleistocene boundaries, as well as the Miocene base were determined.Oligocene NP23 and Miocene NN1 zones are firstly recognized by this study. The existence of Miocene NN1 at this well suggests that the Miocene transgression began in the Early Miocene in this area. The records of NP23 indicate that the marine Oligocene sediments exist in the series of Lingfeng wells, but probably as very thin layers.
基金the Research Grants Council of the Hong Kong Special Administrative Region,China(Grant No.City U 11210419)the Natural Science Foundation of Jiangsu Province(Grant No.BK20200405)the National Natural Science Foundation of China(Grant No.52008098)。
文摘Investigation of dynamic properties of carbonate/calcareous soils is important in earthquake and offshore engineering as these soils are commonly encountered in large-scale projects related with energy geomechanics and land reclamation.In this study,the stiffness and stiffness anisotropy of two types of calcareous sands(CS)from the Western Australia and the Philippines were examined using bender elements configured in different directions in stress path setups.Stiffness measurements were taken on specimens subjected to constant p’compression/extension and biaxial stress paths and additional tests were performed on three types of silica sands with different geological origins and particle shapes,which were used as benchmark materials in the study.Compared with the three brands of silica sands,the stiffness of the CS was found to be more significantly influenced by anisotropic loading;an important observation of the experimental results was that stress anisotropy had different weighted influences on the stiffness in different directions,thus influencing stiffness anisotropy.Comparisons were made between the specimens subjected to complex loading paths,and respected model parameters as suggested from published expressions in the literature.These comparisons further highlighted that calcareous soils have different responses in terms of stiffness,stiffness anisotropy and loading history,compared with that of silica-based sands.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.U1806230 and 42025702).
文摘The shear strength and dilatancy of typical uncemented calcareous sand from the South China Sea are investigated by soil lab tests.According to drained triaxial tests at various relative densities and confining stresses,it is found that the constant volume friction angle is approximated as 39°and the traditional Bolton’s equations can be modified to estimate the peak friction angle and dilation angle.The reliability of the equation proposed for the peak friction angle is verified in terms of calcareous sands from more onshore and offshore sites worldwide,while the errors of the predicted dilation angles scatter in a relatively large range.Totally,the dilation angles of sands in the South China Sea are estimated by the equation presented with an error of±30%.The peak friction angle measured by the undrained is similar to that by the drained tests as the relative density smaller than 60%,while the former is slightly lower for denser samples.
基金supported by the National Natural Science Foundation of China (Nos.41376003 and 41006054)the Strategic Priority Research Program of the Chinese Academy of Sciences (No.XDA13040405)
文摘Cathodic protection is a very effective method to protect metals, which can form calcareous deposits on metal surface. Research on the interrelationship between fouling organism and calcareous deposits is very important but very limited, especially sulfate-reducing bacteria(SRB). SRB is a kind of very important fouling organism that causes microbial corrosion of metals. A study of the influence of calcareous deposit on corrosion behavior of Q235 carbon steel in SRB-containing culture medium was carried out using electrochemical impedance spectroscopy(EIS), scanning electron microscopy(SEM) and surface spectroscopy(EDS). The calcareous deposit was formed with good crystallinity and smooth surface under the gradient current density of -30 μA cm^(-2) in natural seawater for 72 h. Our results can help elucidate the formation of calcareous deposits and reveal the interrelationship between SRB and calcareous deposits under cathodic protection. The results indicate that the corrosion tendency of carbon steel was obviously affected by Sulfate-reducing Bacteria(SRB) metabolic activity and the calcareous deposit formed on the surface of carbon steel under cathodic protection was favourable to reduce the corrosion rate. Calcareous deposits can promote bacterial adhesion before biofilm formation. The results revealed the interaction between biofouling and calcareous deposits, and the anti-corrosion ability was enhanced by a kind of inorganic and organic composite membranes formed by biofilm and calcareous deposits.
基金the National Natural Science Foundation of China(41807102 and U1710255-3)the Shanxi Province Key Laboratory Open Fund of Soil Environment and Nutrient Resources,China(2019003)+1 种基金the Science and Technology Innovation Fund of Shanxi Agricultural University,China(2019004)the Incentive Funding Research Project for Excellent Doctors Settle Down to Work in Shanxi Province,China(SXYBKY201805)。
文摘Soil organic carbon(SOC)plays a key role in improving soil quality and optimizing crop yield.Yet little is known about the fate of macroaggregates(>0.25 mm)under long-term fertilization and their relative importance in SOC sequestration in reclaimed calcareous soil.Therefore,the effects of mineral fertilizers and organic manure on the mechanisms of organic carbon(OC)stabilization in macroaggregates were investigated in this study.Four treatments were used:unfertilized control(CK),mineral fertilizer(NPK),compost chicken manure alone(M),and mineral fertilizers plus manure(MNPK).Samples from the 0–20 cm layer of soil receiving 11-year-long fertilization were separated into four fractions based on the macroaggregates present(unprotected coarse and fine particulate organic matter,cPOM and fPOM;physically protected intra-microaggregate POM,i POM;and biochemically protected mineral associated OM,MOM)by the physical fractionation method.Compared with the control,the long-term application of NPK had little effect on SOC content,total nitrogen(TN)content,and OC and TN contents of macroaggregate fractions.In contrast,incorporation of organic manure(MNPK)significantly increased SOC(45.7%)and TN(24.3%)contents.Application of MNPK increased OC contents within macroaggregate-extracted fractions of cPOM(292.2%),fPOM(136.0%)and iPOM(124.0%),and TN contents within cPOM(607.1%),fPOM(242.5%)and iPOM(127.6%),but not the mineral associated organic carbon(MOM-C)and nitrogen(MOM-N)contents.Unprotected C fractions were more strongly and positively correlated with SOC increase than protected C fractions,especially for cPOM-C,indicating that SOC sequestration mainly occurred via cPOM-C in the studied calcareous soil.In conclusion,MNPK increased the quantity and stability of SOC by increasing the contents of cPOM-C and cPOM-N,suggesting that this management practice(MNPK)is an effective strategy to develop sustainable agriculture.